Using it extensively for my crypto PhD. Several well-known cryptographers contribute to it.
It's an amazing bit of kit. But I'm not without criticisms. I feel it could do with the kind of fresh-start overhaul that really isn't practical for an open-source code base of this nature. E.g. move python 2.6 to python3. Also, you have excellent multi-precision support, but many of the algorithms from other modules don't support precision beyond machine lengths.
But really really good. Love it.